impressive!! Its tough to be a runner and still be left with nice boobs like that, you must have some good genetics
Of course the pushups help too! I dont think they will become a problem for awhile, until you get really old, lol.
Do kids really make the boobs more droopy? Or is that just a result from the woman gaining weight during pregnancy? In any case you dont seem like the type who'd gain a ton of weight. Hitting the gym and working on the arms sounds good, you wont hear me argue with that!